1. Field of the Invention
The present invention relates to a thin film magnetic head comprising a magnetoresistive element using the magnetoresistive effect of a spin-valve film or the like, and particularly to a thin film magnetic head comprising gap layers which are formed above and below a magnetoresistive element and which have improved characteristics, and a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
FIG. 18 is a partial sectional view of a conventional thin film magnetic head, as viewed from the side facing a recording medium. The thin film magnetic head shown in FIG. 18 is a reproducing head (MR head) which is laminated on the trailing side end surface of a slider made of a ceramic material.
In FIG. 18, reference numeral 1 denotes a lower shield layer formed at the lowermost side and comprises a magnetic material such as sendust, permalloy (Nixe2x80x94Fe system alloy), or the like.
A lower gap layer 3 is formed on the lower shield layer 1, and a magnetoresistive element 4 is further formed on the lower gap layer 3. The magnetoresistive element 4 comprises a GMR element, an AMR element, or the like comprising a spin-valve film, i.e., comprises a laminated film 5 utilizing the magnetoresistive effect, and bias layers 6 and electrode layers 7 which are formed on both sides of the laminated film 5.
As shown in FIG. 18, an upper gap layer 8 is formed on the magnetoresistive element 4, and an upper shield layer 9 made of a magnetic material such as permalloy is formed on the upper gap layer 8.
Each of the lower gap layer 3 and the upper gap layer 8 is conventionally made of alumina (Al2O3). This is because alumina is relatively hard and easy to process, and is thus widely used as an insulating material.
However, the conventional thin film magnetic head using alumina for the gap layers 3 and 8 has caused the following problems along with recent increases in recording density.
(1) The first problem is insulation performance. Although the gap layers 3 and 8 are conventionally formed to a thickness of about 60 nm, the thickness of the gap layers 3 and 8 tends to further decrease due to demand for a narrower gap with increases in recording density. For example, with a recording density of 40 Gbit/in2 or more, it is expected that the gap layers 3 and 8 are formed to a thickness of 30 nm or less.
However, with the gap layers 3 and 8 formed to such a small thickness as described above, an appropriate isolation voltage cannot be obtained by the gap layers 3 and 8 made of aluminum. Therefore, in order to maintain insulation performance, the thickness of the gap layers 3 and 8 cannot be decreased to a level which can comply with narrowing of the gap.
(2) The second problem is developer resistance. FIG. 19 is a partial sectional view of the thin film magnetic head taken along line XIXxe2x80x94XIX in FIG. 18, as viewed from the direction of an arrow.
As shown in FIG. 19, a through hole 7a is formed in the upper gap layer 8 on the electrode layers 7, and a main electrode layer 10 is formed to be electrically connected to the electrode layers 7 through the through hole 7a. 
In order to form the main electrode layer 10, the pattern of the main electrode layer 10 is formed on the gap layer 8 by using a resist layer or the like, and the main electrode layer 10 is formed within the pattern.
However, alumina is easily dissolved in a developer such as a strong alkali used for patterning the main electrode layer 10, and thus the etching rate of alumina in exposure to the developer is very high.
Particularly, the thickness of the upper gap layer 8 itself decreases with increases in the recording density in future, thereby causing the serious problem of deterioration in developer resistance.
With low developer resistance, it is difficult to form the upper gap layer to a thickness within a predetermined range, and magnetic insulation between the upper shield layer 11 and the magnetoresistive element 4 cannot be property achieved, thereby deteriorating reliability.
(3) The third problem is a heat radiation property. The density of the current passing through the magnetoresistive element 4 increases with future increases in the recording density, thereby increasing the amount of the heat generated by the magnetoresistive element 4. It is thus expected that the gap layers 3 and 8 have good heat radiation property.
However, the gap layers 3 and 8 made of aluminum are not said to have a sufficient heat radiation property, and the temperature of the magnetoresistive element is increased due to an increase in the current density, resulting in an adverse effect on characteristics.
The above-descried problems (1) to (3) of the gap layers 3 and 8 made of alumina possibly become more serious with further increases in the recording density.
Although alumina has relatively good properties, the gap layers 3 and 8 are further required to have smoothness.
Particularly, the lower gap layer is required to have the smoothness. It is known that when the magneoresistive element 4 is a spin-valve thin film element, the occurrence of unevenness on the surface of the lower gap layer 3 increases the interlayer coupling magnetic field (Hbf) between a free magnetic layer and a pinned magnetic layer which constitute the spin-valve thin film element, thereby decreasing the rate (xcex94MR) of change in resistance.
As described above, the gap layers 3 and 8 made of alumina cannot satisfy all the insulation performance, the developer resistance, the smoothness, and the heat radiation property.
The present invention has been achieved for solving the above problems, and it is an object of the present invention to provide a thin film magnetic head comprising a gap layer made of an Alxe2x80x94Sixe2x80x94O film or Alxe2x80x94Sixe2x80x94Oxe2x80x94N film for improving the insulation performance, the developer resistance, the smoothness, and the heat radiation property of the gap layer, and a method of manufacturing the thin film magnetic head.
The present invention provides a thin film magnetic head comprising a lower shield layer, a lower gap layer formed on the lower shield layer, a magnetoresistive element formed on the lower gap layer, an upper gap layer formed on the magnetoresistive element, and an upper shield layer formed on the upper gap layer, wherein the lower gap layer and/or the upper gap layer is made of an insulating material represented by the composition formula Alxe2x80x94Sixe2x80x94O wherein the Si content is 2 at % to 9 at % of the total.
The present invention uses, as a gap layer, a conventional Alxe2x80x94Sixe2x80x94O film composed of the components (Al and O) of alumina and Si added thereto, whereby the insulation performance, the developer resistance, the smoothness, and the heat radiation property of the gap layer can be improved.
The results of experiment described below indicate that the amount of Si added is preferably 2 at % to 9 at % of the total. The addition of Si improves the isolation voltage of the Alxe2x80x94Sixe2x80x94O film, as compared with alumina. For example, Al34.0Si5.0O61.0 having a thickness of 30 nm has an isolation voltage of 7.7 MV/cm. The isolation voltage of alumina is 4.0 MV/cm.
The developer resistance is also improved, as compared with alumina. Although the etching rate of alumina is about 50 xc3x85/min, the etching rate of the Alxe2x80x94Sixe2x80x94O film is decreased to a value close to 0 xc3x85/min due to the addition of about 9 at % of Si.
The conceivable cause of improvements in the insulation performance and the developer resistance of the Alxe2x80x94Sixe2x80x94O film as compared with alumina is that SiO2 generally known as an insulating material other than alumina has high insulation performance and high developer resistance, and thus the insulation performance and the developer resistance of the insulating material composed of Al and O and Si added thereto are improved by Sixe2x80x94O bonding.
The smoothness is also good, and the same degree of smoothness as alumina can be maintained.
Furthermore, the heat radiation property is superior to alumina, and thus the element temperature can be sufficiently suppressed even when the current density increases with future increases in the recording density.
The possible cause of improvement in the heat radiation property as compared with allumina is that the atomic arrangement of the Alxe2x80x94Sixe2x80x94O film has short-range order. Although alumina has a completely amorphous structure, the Alxe2x80x94Sixe2x80x94O film exhibits short-range order in the atomic arrangement as the amount of Si added is increased, and thus crystallinity is supposed to be improved. A decision as to whether or not short-range order occurs in the atomic arrangement can be made by observing a transmission electron beam diffraction image.
In the present invention, Si is preferably added to the Alxe2x80x94Sixe2x80x94O film so that when Si is converted into SiO2 in a stoichiometric manner, the SiO2 amount in the film is 10 at % to 38 at %.
In the present invention, Si is more preferably added to the Alxe2x80x94Sixe2x80x94O film so that when Si is converted into SiO2 in a stoichiometric manner, the SiO2 amount in the film is 6.1% by mass to 26.0% by mass.
In the present invention, the insulating material may further contain N and may be represented by the composition formula Alxe2x80x94Sixe2x80x94Oxe2x80x94N wherein the N content is 2 at % to 10 at % of the total.
The insulation performance of the Alxe2x80x94Sixe2x80x94Oxe2x80x94N film is slightly lower than the Alxe2x80x94Sixe2x80x94O film, but the isolation voltage is higher than that of alumina.
The etching rate of the Alxe2x80x94Sixe2x80x94Oxe2x80x94N film is substantially the same as the Alxe2x80x94Sixe2x80x94O film, and the heat radiation property of the former is superior to that of the latter. The experimental results of various properties of the Alxe2x80x94Sixe2x80x94Oxe2x80x94N film will be described in detail below.
In the present invention, the Alxe2x80x94Sixe2x80x94O film or Alxe2x80x94Sixe2x80x94Oxe2x80x94N film is preferably formed to a thickness of 10 nm to 60 nm. It was confirmed that even when a gap layer is formed to such a small thickness, the insulation performance, the developer resistance, and the smoothness can be sufficiently maintained.
In the present invention, in observation of a transmission electron beam diffraction image, short-range order is preferably observed in the atomic arrangement of the Alxe2x80x94Sixe2x80x94O film or Alxe2x80x94Sixe2x80x94Oxe2x80x94N film. The occurrence of short-range order in the atomic arrangement means that crystallinity is improved, and particularly the heat radiation property of the gap layer can be improved.
The present invention also provides a method of manufacturing a thin film magnetic head comprising a lower shield layer, a lower gap layer formed on the lower shield layer, a magnetoresistive element formed on the lower gap layer, an upper gap layer formed on the magnetoresistive element, and an upper shield layer formed on the upper gap layer, the method comprising forming a target composed of AlSi, and introducing O2 gas into a sputtering apparatus to form the lower gap layer and/or the upper gap layer represented by the composition formula Alxe2x80x94Sixe2x80x94O wherein the Si content is 2 at % to 9 at % of the total.
In the present invention, N2 gas may be further introduced into the sputtering apparatus to form the lower gap layer and/or the upper gap layer represented by the composition formula Alxe2x80x94Sixe2x80x94Oxe2x80x94N wherein the N content is 2 at % to 10 at % of the total.
In the present invention, the target can be made of AlSi so that the Si amount can be set only by controlling a mixing ratio to Al. Also, the O2 gas and further the N2 gas are introduced into the sputtering apparatus so that the Alxe2x80x94Sixe2x80x94O or Alxe2x80x94Sixe2x80x94Oxe2x80x94N film having a predetermined composition can easily be formed by reactive sputtering process.